1. Field of the Invention
The present invention relates to an inkjet recording medium suitable for recording an image by applying ink thereto by an inkjet process, and to an inkjet recording method.
2. Description of the Related Art
In an inkjet recording system ink droplets ejected from an ejecting outlet of a recording head are adhered onto a recording medium such as paper to record an image thereon.
In inkjet recording, in particular, in color inkjet recording, a high degree of ink absorbancy is required for recording materials due to the use of a large amount of aqueous ink. As a recording material suitable for inkjet recording which has excellent ink absorbancy, a recording material is known in which a porous ink receiving layer containing a pigment such as amorphous silica and a water-soluble resinous binder such as polyvinyl alcohol is provided on a support.
In recent years, recording materials with a photo-like glossiness using inorganic ultra-fine particles as a pigment have been developed. For example, it has been proposed to use, as a pigment component for an ink receiving layer, inorganic ultra-fine particles of fumed silica, precipitated silica and the like that have been pulverized to a size of 500 nm or less and dispersed. For examples of fumed silica used in this manner, see Japanese Patent Publication No. 3-56552 and Japanese Patent Application Laid-Open (JP-A) Nos. 10-19423, 2000-211235 and 2000-309157; for examples of use of silica produced by a method including pulverization and sedimentation, see JP-A Nos. 9-286165 and 10-181190, and for examples of use of silica produced by a pulverization gel method, see JP-A No. 2001-277712. Recording materials using alumina or alumina hydrates have also been disclosed (for example, see JP-A Nos. 62-174183, 2-276670, 5-32037 and 6-199034).
However, when inorganic ultra-fine particles such as these are used, although a high degree of glossiness and a high degree of ink absorbancy may be obtained, the viscosity of a coating liquid tends to increase. Therefore, the coating liquid has to be coated and dried at a low solid concentration. In particular, in recent years, in order to obtain high glossiness and an excellent texture that resembles that of photographic printing paper, or to prevent the occurrence of cockling in recording materials due to a large quantity of ejected ink, polyolefin resin-coated paper (wherein both surfaces of a paper substrate are laminated with a polyolefin resin such as polyethylene) is suitably used. However, in resin coated paper such as this, it is necessary to apply and dry a larger amount of a coating liquid at a low solid concentration, since the support cannot absorb ink, and therefore, there is a problem that productivity cannot be increased.
Further, it is known that inkjet recording materials using polyolefin resin-coated paper exhibit inferior sheet conveyance properties and inferior accuracy in conveyance in a printer, compared with inkjet recording materials that use paper as a support.
One problem with paper conveyance is that a paper coated with a polyolefin resin cannot be conveyed to a predetermined position for printing in a printer with high accuracy, and tends to cause non-feeds (feeding malfunctions), resulting in difficulties with successive printing. In general, inkjet recording materials are stacked on a paper feed tray in an inkjet printer, and one important property of a recording material is favorable paper feedability, namely, that the recording material may be smoothly fed from a paper feed tray to a printer main body.
Further, inkjet recording materials using inorganic ultra-fine particles are extremely susceptible to external stress, since ink absorbancy of the coating layer is increased, which leads to another problem relating to paper feedability, namely that, when several tens of sheets are stacked and successively printed, the ink receiving layer, which is the front side surface of a recording material, is damaged by the back side surface of another recording material. Polyolefin-coated paper is often designed to have a high rigidity in order to obtain a texture similar to that of silver salt photographic printing paper. Accordingly, inkjet recording materials using polyolefin-coated paper may cause paper feed malfunctions and, further, polyolefin resin-coated paper is often used for photographic printing paper, and since it often contains pigment particles in a back coating layer formed on the back side thereof, there is a problem that a paper is damaged by the pigment particles during successive printing.
With regard to problems of sheet feeding accuracy, when sheet feeding accuracy is low, a portion of a recording material in which an image is to be printed is conveyed to a position deviating from a predetermined printing position. Consequently, favorable printing quality may not be achieved due to the occurrence of streaked unevenness along a main scanning direction of a scanning head in a background solid area or the like, known as banding, or the occurrence of streaked non-printed portions along the main scanning direction of a scanning head, known as white deletion.
Here, with reference to FIG. 1, a paper feed mechanism in a common inkjet printer will be schematically explained. As shown in FIG. 1, an inkjet printer is equipped with a paper feed roller 1. The paper feed roller 1 is formed from a pair of rollers: a drive roller 2 that contacts a back surface of a recording material M, and a driven roller 3 that contacts a front surface (recording surface) of the recording material M. The inkjet printer is further equipped with a platen 4 and a recording head 5. The drive roller 2 is rotatably driven by a drive motor as a drive source and the number of revolutions thereof is simultaneously controlled, and the driven roller 3 is rotated in accordance with the rotation of the drive roller 2. The recording material M is nipped by nip portions of the rollers, and conveyed to a position of the platen 4, and the feed amount thereof is simultaneously controlled in accordance with print data transmitted from a host computer or the like. At the position of the platen 4, ink ejection from the recording head 5 is performed in synchronization with the control of the feed amount, by which ink is adhered on the recording material in each unit area according to a predetermined pattern to form an image.
In such a paper feed mechanism, it is important that the feed amount of recording material by the feed roller 1 is controlled with a high degree of accuracy. If the accuracy of control of the feed amount is low, positions at which ink droplets are impacted may deviate from their intended positions, which may result in the occurrence of banding or white deletion. Therefore, in order to perform paper feeding with a high degree of accuracy, a roller having a surface with asperity (surface asperity roller) has been adopted as the drive roller 2 that constitutes the paper feed roller 1. Since the surface of the surface asperity roller that comes in contact with a recording material has a high static friction coefficient, the roller can ensure a sufficient static friction coefficient even for a slippery material such as film, and can convey the recording material with high accuracy.
However, when an inkjet recording material using a polyolefin resin-coated paper is used in such a printer which is provided with a surface asperity roller as a paper feed roller (drive roller), and which is expected to perform conveyance with a high accuracy, slippage tends to occur between a back coat layer on a back side of the recording material and the drive roller. For this reason, problems occur such as reduction in sheet feeding accuracy or the occurrence of banding or white deletion.
In relation to the above, various studies have been made regarding improvements in accuracy of sheet feeding in a printer. For example, a technique of coating a back surface of a recording material with a solution formed by mixing tabulate delaminated kaolin clay and hydrated aloisite with a modified PVA and an SBR (Tg=29.5° C.) has been proposed (for example, see JP-A No. 6-278357).
In order to control the feed amount in a feed system employing a metal roller, laminating a back coat layer on a back surface opposite to a recording surface of a recording material has been proposed (for example, see JP-A No. 7-276781). Further, a technique of applying a mixture of colloidal silica with an average particle diameter of 0.5 μm or less and a resin for adhesion at a ratio of 40:100 on a back surface of a recording material at an amount of 5 g/m2 has been proposed (for example, see JP-A No. 2000-6513). Further, it has been proposed that a composition containing 70% by mass or more of a polyurethane resin (Tg=−10° C. to 120° C.) with respect to the total solid content of a back coat layer is applied onto a recording material at a thickness of from 0.6 μm to 1.5 μm (see, for example, JP-A No. 2005-205765).
However, in the technique disclosed in JP-A No. 6-278357, the ratio of inorganic fine particles to PVA and SBR is high, and the coating amount is also large, and therefore feeding accuracy during high speed printing may decrease due to a low static function coefficient with respect to a metal roller, even though paper feeding properties with respect to a pickup roll are excellent. Additionally, as described above, in a recording material having a back coat layer simply laminated on a back surface opposite to a recording surface, the static friction coefficient between the front surface and the back surface may not be taken into account, and thus there is a possibility that double feeding, in which two sheets are fed into a printer at the same time, may occur. Further, there is no clear discussion on polymer materials used for the back coat layer, and the feedability may even be worsened by the provision of a back coat layer.
In the technique of applying a mixture of colloidal silica and a resin for adhesion at a predetermined ratio to a back surface of a recording medium, a large application amount thereof causes deposition of a fine powder of colloidal silica onto portions of a metal roller having asperity due to continuous operation, resulting in decreased feeding accuracy due to a decrease in the static friction coefficient between the metal roller and the back surface of the recording medium.
Further, as described above, when a given amount or more of a polyurethane resin is used for a coating with a given thickness, the rigidity of a support and a requisite static friction coefficient for the support, as well as an amount of deformation due to the impression of a metal roller to a back surface of the support are not taken into account, even though the range of the rigidity that is applicable to a support may have been defined. Consequently, banding cannot be prevented, and the feeding accuracy is low when printing is performed at high speed due to a small coating amount of the resin on the back surface.
Meanwhile, recent years have seen continuing increases in speed of the operations of printers, and information recording at a higher speed in an inkjet printer has been desired, and consequently there is a demand for further improvement in the feeding accuracy of a recording material in order to maintain a high quality for printed images.
In order to make a recording material applicable for inkjet recording wherein the recording material is fed by a metal roller onto which wear-resistant particles are uniformly adhered, there is a need for the metal roller to hold the recording material at a back surface thereof in an appropriate manner.
Although commercially available recording materials for inkjet recording have applicability to inkjet printers on the market, when the recording speed increases, feeding accuracy may decrease due to insufficient gripping force.